Low cost, small sized navigation grade gyroscopes for commercial navigation applications are preferred. Among optical gyroscope technologies, resonator fiber optic gyro (RFOG) could potentially satisfy those needs by providing better signal to noise sensitivity to rotation rate measurement than the existing interferometric fiber optic gyroscopes (IFOG) and the ring laser gyroscopes (RLG).
In conventional RFOGs, a ring resonator is formed using a fiber optic coil and at least one coupler to couple light into and out of the resonator in clockwise and counterclockwise directions. At least two input light waves are frequency-tuned to the resonances of the resonator in the clockwise and counterclockwise directions respectively. After measuring the resonance frequencies in the two directions by tuning each input beam to them, the input beam frequencies are compared, and the difference is proportional to the rotation rate of the resonator coil.
Some conventional RFOGs use glass core fibers. To get a better signal to noise ratio, the power of the light signal received by the RFOG is increased. However, because of the refractive index of the glass, high power can cause lasing due to Brillouin scattering within the glass core fiber. Accordingly, some RFOGs use hollow core fibers that do not have glass in the core.
However, one of the major issues in conventional RFOGs is bias instability; that is, an indicated output when the gyroscope is not rotating. One of the major causes of this bias instability in RFOGs is that light that is intended to be introduced into the resonator is not matched properly into it. When using practical Hollow Core Fiber (HCF) for the resonator, this improperly matched light excites higher order modes in the HCF resonator, causing bias errors.
For the reasons stated above and for other reasons stated below, it will become apparent to those skilled in the art upon reading and understanding the specification, there is a need in the art for methods and systems that reduce errors in the RFOGs using hollow core fiber.